A question regarding The Shawshank Redemption?

I made a bet with someone in my school concerning the movie The Shawshank Redemption. The other kid said that Brooks Hatlen got out of the prison in the 1970's. Of course I knew this was 100% wrong and he sounded so sure of himself. I know I am right but I can't find proof off the internet (even wikipedia). Where can I find the answer to when Brooks got out of jail?